Bat an eyelid

A The bat in the expression turns out to have nothing do to with nocturnal flying mammals. And likewise it’s unconnected with table-tennis, cricket, baseball or any other game in which a bat is an essential requirement.

Three idioms are associated with batting eyes or eyelids, by which we mean a pronounced rapid blink or series of blinks.

One — very old-fashioned — is I didn’t bat an eyelid all night, equivalent to I didn’t sleep a wink. If a woman bats her eyelids (more commonly her eyelashes) she’s fluttering them flirtatiously:

It was amusing to watch the woman — who must have been at least sixty — dissolve into girlish simpering in the wave of my brother’s considerable charm. When she began coyly batting her eyelashes at him, I'd had about all I could stand of this stomach-turning display.

The Cliff House Strangler, by Shirley Tallman, 2007.

The third, not to bat an eye (or eyelid) is to avoid blinking or showing any other emotion when something awkward occurs, a mark of self-control and equanimity.

For the answer, we must look to the long defunct verb, bate, which is connected to our abate, debate and bated breath. It came into English from French battre, to beat, and meant, among other things, the beating or fluttering of a falcon’s wings. Over time, bate became shortened to bat in some English dialects and came to mean “blink” or “wink”. Dialect researchers in the nineteenth century noted this sense of bat in a swathe of England from south Yorkshire down to Nottinghamshire and across to Shropshire.

The sense of flirtatiousness is originally American. It starts to appear in the record around 1880.

You hol’ your head high; don’t you bat your eyes to please none of ’em.

At Teague Poteet’s, by Joel Chandler Harris, in the Century Illustrated Monthly Magazine, May 1883. This story of Georgia backwoodsmen and moonshiners was published the following year in Mingo and Other Sketches in Black and White.

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